Method and system for identifying documents generated by an unauthorized software copy

摘要

Each copy of software is assigned a unique identifying code pattern which is printed on all documents produced with that software by a high resolution printer. The unique identifying code pattern is a plurality of spaced apart marks having a size no greater than about 300 dpi, and is therefore, at best, barely noticeable to the human observer. The "invisible signature" is also reproduced on documents made by unauthorized copies of software which can therefore be traced. Preferably, the unique identifying code is replicated multiple times over the document using an error correcting code to assure that at least one replication will be clear of matter selected for printing by the software. A high resolution scanner extracts and identifies the code patterns printed on the document. In systems where the software generates a print file for the high resolution printer, print commands for the pattern replications are interspersed with the other print commands making identification and removal of the commands very difficult and not worth the effort since the "invisible signature" does not prevent copying of the software or noticeably detract from the appearance of the finished document.